The shooting occurred at about 10:30 p.m. ET inside a third-floor apartment at 40 Turf Grassway, a low-rise Toronto Community Housing building located just south of Jane Street and Finch Avenue West.
Toronto police said Tuesday they responded to a call about a shooting at 10:33 p.m. When they arrived, they found a boy, 15, "suffering from an obvious gunshot wound."
There were reports the victim was shot in the stomach. He was taken to hospital by Toronto Emergency Medical Services without vital signs.
Police said the victim's name wasn't being released at this time. There was no word on arrests.
CBC's Trevor Dunn spoke to a woman Tuesday who lives on the same floor where the shooting took place. She didn't want to be named, but she described what she heard at the time of the shooting.
"I heard some big noise, like people running," she said.
Neighbours said they were frightened after learning about the fatal shooting in their building.
"I'm feeling scared right now to live in the neighbourhood," said one woman. "I don't feel safe, not with this around."
A friend of the victim's told CBC News the boy went by the name "Tubby." Notices of condolence were posted on social media site on Monday evening to someone of the same name.